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Tansy Ragwort

Photo: Michael Shephard, USDA Forest Service, Bugwood.org

Photo: Leslie J. Mehrhoff, University of Connecticut, Bugwood.org

What is it?

Tansy ragwort is a biennial herb that grows well in disturbed sites such as roadsides, forests that have recently been logged, and pastures. It is native to Europe and western Asia. It often spreads through contaminated hay. Because it also contaminates milk, it poses potential toxic risks to humans as well.

Is it here yet?

Yes, tansy ragwort has been well documented throughout Washington.

Why should I care?

Tansy ragwort can cause severe economic impacts to farmers and ranchers, as it is one of the most common causes of poisoning in cattle and horses when consumed in pastures or hay.

What should I do if I find one?

How can we stop it?

Clean equipment and vehicles before moving them out of an infested area. Tansy ragwort is on Washington’s Terrestrial Noxious Weed Seed and Plant Quarantine list, meaning it is prohibited to transport, buy, sell, offer for sale, or distribute plants, plant parts, or seeds (Washington Administrative Code 16-752-610). It also is listed as a Class B noxious weed in Washington, meaning it is designated for control in certain state region.

What are its characteristics?

The plant's stem is stout, erect, or slightly spreading, and may be branched; often groups of stems arise from the plant crown.

Its leaves are dark green on top, whitish-green underneath, and have deeply cut, blunt-toothed lobes with a ragged/ruffled appearance.

Flower clusters develop on stout, leafy, elongated stems that grow up to 6 feet tall; each flower cluster is composed of many bright-yellow flowers with (usually) 13 petals.

Its seeds have a white pappus and are wind-carried, resulting in rapid infestations.

How do I distinguish it from native species?

Common Saint Johnswort (Hypericum perforatum) and common tansy (Tanecetum vulgare), are Class C noxious weeds in Washington may be mistaken for tansy ragwort. Common Saint Johnswort also is found roadside, has yellow flowers, but it has five petals. Common tansy has yellow globes without petals. If you need help with plant identification, contact your county noxious weed coordinator.